Melting control device



Oct. 4, 1966 R. L. SCHULTZ MELTING CONTROL DEVICE 2 Sheets-Sheet 1 Filed Oct. 14, 1963 m a M W 7 W. a n w a A 7 o H a m. m L w a M 4 J f 4 Eat;

INVENTOR.

A rro/wvzrs 2 Sheets-Sheet 2 Oct. 4, 1966 R. L. SCHULTZ MELTING CONTROL DEVICE Filed Oct. 14, 1965 United States Patent ice 3,276,692 MELTING CONTROL DEVICE Robert L. Schultz, Decatur, Ala., assignor to Calumet & Hecla, Inc, Allen Park, Mich, a corporation of Michigan Filed Oct. 14, 1963, Ser. No. 315,860 23 Claims. (Cl. 236-) The present invention relates to an improved melting control device for induction or like furnaces containing a molten metal mass or bath. The purpose of the device is to automatically maintain, with desired limits, the amount of metal in the furnaces melting container that is in a liquid, semi-solid or solid state. The device does this by utilizing the variable mechanical resistance of the metal in these states to penetration by a moving test object. An electrical control system operates in response to limit switch signal from the object to regulate the application of heat to the furnace, as by operating its highand low-heat circuit breaker transformer connections, thus automatically to maintain a desiredly molten condition of the metal bath in the furnace.

A general object of the invention is to provide a control device of the above sort which makes a sampling of the metal bath by periodically plunging a feeler or test rod into the latter for the purpose of physically determining when it has partially solidified to an extent to resist motion of the rod to a predetermined depth in the bath in a predetermined time interval. When failure of the rod to reach depth in the pre-set time occurs, the device of the invention, through its improved electrical limit switch and timing and control relay circuit, changes the breaker taps from a low power furnace heat input to a high power input, thus to melt out the metal to its desired condition of viscosity in the zone of travel of the test object or rod.

A further object is to provide a melting control device as described which is, structurally speaking, of very simple and inexpensive nature, being also readily applicable in proper operating location relative to a wall of the melting vessel of the furnace, for an oscillatory action of its test or feeler rod in a predetermined path in the molten bath.

The invention also provides relatively simple and reliable electrical circuitry, including limit switch, control relay and timing relay provisions for automatically cutting the furnace heat control circuit breaker off normal low power transformer output and onto high transformer output when the motion of the feeler is more than predeterminedly resisted or obstructed due to partial freezing or solidification of the metal bath in the feeler zone. This results in a failure in a pre-set time of the feeler or test rod to open a normally closed limit switch of the control circuit, whereupon the circuit operates to automatically increase furnace heat until the limit switch is opened by the feeler in the allotted time interval. The circuit then restores the furnace heating system to normal low power.

In regard to mechanical or structural features of the device, the latter is comprised of a support adapted to be suitably mounted to the furnace, a vertically oscillatory test feeler or sampling rod pivotally mounted on the support and normally weight-counterbalanced in a direction to lift the same out of the bath, and an electrical solenoid to swing the feeler rod down into the bath upon electrical signal from the melting control circuit, the solenoid being mounted upon the support for the oscillatory rod and connected to the latter to guide the same by means of an upwardly extending bar or strap.

In regard to the control circuit, per se, it includes the normally closed limit switch which, as indicated above,

Patented Get. 4, 1966 is opened at pre-set intervals when the metal bath or mass is adequately molten. As operated under the control of such feeler-responsive limit switch, the electrical circuitry essentially comprises a breaker control relay whose normally closed and open contacts will be wired, respectively, to the low heat and high heat taps of the furnace transformer breaker. Thus, with this control relay deenergized as the result of opening of the limit switch when proper fluidity of the bath exists, the furnace breakers low heat circuit is closed and its high heat tap is open. But upon energization of the control relay if the limit switch is closed or remains closed, the breaker high power tap is energized to further heat and melt the bath.

All of this takes place under the control of timing relays, including one which is set to operate certain normally open contacts thereof at predetermined intervals of, say, three minutes each, and to operate other normally open contacts thereof at intervals of, say, one minute. Thus, at three minute intervals individual energizing circuits are completed (always under the basic control of the limit switch), for the test or feeler rod-operating solenoid and for the breaker control relay. Should the feeler fail to open the limit switch of the circuit in the feelers predetermined sweep time, the circuit breaker goes onto or remains on high tap power until the limit switch opens. At such times the feeler operating solenoid is de-energized and the feeler rod is counterbalanced out of the bath.

While the furnace is on high heat, the normally open one minute contacts of the relay referred to in the preced ing paragraph periodically complete circuits to occasion audible and visible signals at one minute intervals, thus warning an attendant that high heat operation is in effect.

Also included in the improved melting control circuit, as a safety provision, are further emergency timing relay means automatically operative to restore the furnace circuit breaker to low heat tap in the event it does not do so, as operated in a normal way by other provisions above referred to, within a predetermined, relatively lengthy time interval of, say, seven minutes; and this auxiliary safety circuitry also at this time sets up continuous audible and visible alarm signals, at the means previously mentioned.

The foregoing as well as other objects will become more apparent as this description proceeds, especially when considered in connection with the accompanying drawings illustrating the invention, wherein:

FIG. 1 is a side elevational view, more or less schematic, of the mechanical structure of the improved solenoid-operated solidification control device, showing its oscillatory testing or feeler rod in operative testing and withdrawn positions in solid and dotted lines, respectively;

FIG. 2 is a top plan view of the device of FIG. 1;

FIG. 3 is a schematic wiring diagram of the improved electrical melting control circuit, showing limit switch, control relay and timing relay provisions of the latter as associated with the feeler actuating solenoid and certain audible and visible signal and alarm means; and

FIG. 4 is a schematic view, partially broken away and in vertical section through the well-insulated melting vessel of an induction heated furnace equipped with the melting control provisions of the invention.

Referring to FIGS. 1 and 2, the device of the invention, generally designated 10, is structurally very simple. It comprises a rigid mounting support 11 constructed of welded lengths of channel stock, including a horizontal base piece 12, an upright piece 16 and a top horizontal piece 14, these pieces being welded together at right angles to provide the generally Z-shaped support 11. Intermediate its length, the top member 14 has a depending rod 15 welded thereto, which may be attached i) rigidly to the wall of the furnace melting vessel V of a furnace F, as by the means schematically suggested in FIG. 4, thus rigidly supporting the base 12 and upright 13 on the exterior of the furnace wall.

Within upwardly facing flanges of the top support piece 14 (FIG. 2), a pair of upright, laterally spaced strap or bar members 17 are welded to its horizontal web, member 17 furnishing a pivotal support for generally horizontal oscillatory rocker arm 18. This arm may be constituted by a pair of elongated, parallel steel bars or straps 19 receiving a pin 20 to pivot the same on the upright members 17 adjacent the top of the latter, with an appropriate interposed spacer 21 surround-ing pivot pin 20.

At their outer or left-hand end, the straps 19 of elongated rocker 18 receive a testing or feeler rod 22 therebetween, the rod being rigidly secured to the rocker, as by welding to the straps 19. Rod 22 includes an upper portion 23 paralleling and extending substantially forward of its connection to rocker straps 19, i.e., sufiiciently to position the rod for oscillatory immersion in the molten bath at a suitable representative location of the latter; and rod 22 is bent downwardly at a downwardly projecting testing portion 24 of substantial length, i.e., portion 24 is of sufiicient height to have a downward testing sweep through a substantial mass of the molten metal. At least the portion 24 of feeler rod 22 is ceramic encased or otherwise fabricated to protect against heat damage. FIG. 4 arbitrarily shows the bath in the furnace vessel V as including an upper volume v which will tend to solidify earlier than a lower volume v At its opposite end the elongated rocker 18 has a counterweight 25 mounted thereon and normally operative to swing testing rod 22 upwardly about pivot pin 20 to the withdrawn, dotted line position of FIG. 1, assuming that the bath is of suflicient molten fluidity that the electrical contact circuitry of FIG. 3 is not brought into play. Such upward withdrawal of course occurs only upon the timed de-energization of the electrical operating solenoid 27 of device 10.

In order to mount the solenoid 27, the base 12 of support 11 carries a bracket structure 28 which fixedly mounts the body of solenoid 27; and a core plunger or armature piece 29 of the solenoid extends upwardly through a horizontal part of bracket 28. At its top the plunger 29 is pivotally connected at 30 to an upright strap or bar 31; and this bar is in turn pivotally connected at its top to the rocker 18 at a point between the rocker pivot pin 20 and the counterweight 25, as by a pivot pin 32 extending through rocker bars 19.

So long as the test rod 22 is able to reach depth and (through some part suitably connected to move therewith) trip a normally closed limit switch 34 (FIGS. 3 and 4), as by the engagement of its operating finger 34' by a projecting lug 34" on plunger strap 31, to momentarily open the same, the solenoid 27 will be periodically energized, upon re-closure of the switch and through timer means to be described, to continue the periodic downward sweeps of tester or feeler 22, each of pre-set duration. Limit switch 34 may conveniently be mounted adjacent solenoid 27 on base 12 of the support 11, as shown in FIG. 4.

Now referring to FIG. 3, the overall circuit for the controlled energization of solenoid 27, as well as of the circuit breaker (not shown) for the furnace transformer, is generally designated by the reference numeral 36. As shown in FIG. 4, such transformer may be considered to be represented by an insulated primary induction coil C to in turn energize and heat a secondary constituted by a circulatory portion v of the molten metal at the bottom of melting vessel V. However, the furnace may be heated by other means, induction or equivalent, controlled in a known manner by a circuit breaker or equivalent circuit-establishing provision. Such breaker means is electrically supplied by parallel power leads or lines 37 and 38 of the circuit of FIG. 3, the latter grounded at 39, from an appropriate 115 volt source. The contact 40 of a master on-ofr" control switch and a limiting fuse 41 are wired in the input line 37.

A master timing relay TRI is connected across supply lines 37, 38; and this relay, when energized, closes and opens a pair of its normally open contacts TR-la and TR-lb at intervals of, say, three minutes. Timer TR-l also controls a further pair of normally open contacts TRlc and TR-ld to close and open the latter at intervals of one minute. The timer and its contacts are Wired in circuit 36 in a manner to be describe-d to respond to the closed feeler-responsive limit switch 34.

One terminal of the limit switch is connected to supply line 37, and a second timing relay TRZ is connected between the other terminal of the limit switch 34 and the line 38. Timing relay TR-2 is a pneumatic timer having an adjustable range of from two seconds to sixty seconds; and it operates only one normally open contact TRZa, which is wired in series with a first control relay CR1 across the leads 37, 38. Timer TR2 acts, as adjustably set, to fix a predetermined time interval for a full downward sweep of feeler rod 22 into the metal bath when the latter is of intended molten consistency.

The control relay CR1 operates a pair of normally open contacts CR1a and CR-lb. Contact CR-la is connected between the common tap of limit switch 34 and timer TR2 and a terminal of the normally open, three minute contact TR-la of pneumatic timer TR2. The other terminal of the last named contact is connected to a normally closed contact TR3a of a safety timing relay TR3, the function of which will be described; and contact TR3a is in turn connected in series through a second control relay CR-2, which is the breaker control relay of the system, with the return line 38.

There are a pair of normally open and normally closed contacts governed by breaker control relay CR-2. These contacts do not appear in FIG. 3, but of the two, the normally closed contact is wired to energize the low heat tap of the breaker control circuit of the furnace system when control relay CR-2 is de-energized; and the normally open contact of the two is wired to the high heat tap of the breaker circuit to energize that tap when control relay CR2 is energized and the contact closed.

A third, lock-in control relay CR3 is connected to line 38 in shunt about contact TR3a and relay CR2; and the first, normally open contact CR-3a of relay (IR-3 is shunt-connected about the timing relay three minute contact TR-la. Thus a series sub-circuit, designated A, for the control of the furnace breaker through its relay CR-2 is set up across lines 37, 38, the circuit A including limit switch 34, contacts CR-la, TRla, TR3a and control relay CR-Z.

The safety timing relay TR3 for the normally closed contact TR-3a is wired between line 38 and the common connection of contacts TR3a and TR-la. Timer TR3 is a ten minute timer, set in the present instance to time out and open its contact TR-3a in a period of, say, seven minutes, thus de-energizing breaker control relay CR-2 and dropping the furnace to low heat. In addition to normally closed contact TR3a, safety timer TR3 controls a normally open contact TR-3b wired in a signaling circuit, to be described.

The operating solenoid 42 of an electrical clutch 43 is connected in parallel With safety relay TR3 to the return line or lead 38, this clutch not being involved in the operation of circuit 36 as such. Actually, it functions in the reduction of heat of the furnace upon a timing out of timer TR3.

A sub-circuit, generally designated B, for the control of the feeler operating solenoid 27 includes, in series with the latter across the leads 37, 38, a second normally open contact CR-lb of relay CR-l, a second normally open, three minute contact of main timer TR-l and a second normally closed contact CR3b of the lock-in control relay CR-3. A shunt line about contacts TR-lb and CR-3b connects a third normally open contact CR3c and one of the one minute contacts TR-lc of main timer TR-l in series with the return lead or line 38.

A timer signaling and alarm circuit, generally designated C, is in effect when the furnace breaker is tapped to high heat. This sub-circuit C extends across leads 37, 38 and includes a second one minute contact TR-ld of main timer TR-l, a fourth, normally open contact CR-3d of locking relay CR-3 and a horn 44 or other audible signal unit. The contacts TR1d and CR-3d are shunted by the second, normally open contact TR-3b of the safety timing relay TR-3; and a signal light 45 is connected in parallel with the horn 44 in the signaling sub-circuit C;

In the operation of this circuit, the contacts TR-ld and CR-3d close in the normal high heat setting of the circuit 36 to set up one minute-timed energizations of horn 44 and light 45 to indicate that the furnace is properly on high heat. However, when safety timer TR3 times out after seven minutes, its contact TR-3b closes and continuing audible and visible signals are produced at the components 44 and 45 to alert an attendant.

In operation, assuming that master switch contact 40 is closed to energize the timing relay TR1, and that there is a bath of sufiiciently molten metal in the furnace to permit the feeler rod 22 to pass in a full downward sweep in the metal (in the time allotted by pneumatic timer TR2) to momentarily open limit switch 34, the control relays CR2and CR-3 are dc-energized, since the contact TR-2a of timer TR2 is open to de-energize control relay CR1. With breaker control relay CR-2 de-energized, its lowheat contact (not shown) remains closed and its high heat breaker contact (also not shown) remains normally open.

On the other hand, if there is a sufliciently solidified mass of molten metal in the furnace melting vessel to prevent the feeler 22 from penetrating the metal bath to open limit switch 34 in the limited time, the timer TR-l, as energized upon and during closure of master contact 40, closes its contacts, one of which (the three minute timer contact TR-la) partially completes the sub-circuit A for breaker control relay CR-2.

With limit switch 34 closed, a circuit is also completed through feeler timer TR-Z and, after the p're-set timing period of the latter, its single contact TR-Za closes, thus energizing control relay CR-l. This completes energizing circuit A through breaker control relay CR-2 as previously traced.

Control relay CR-3 is also energized to close its normally open contact CR-3a and complete a locking circuit for breaker control relay CR-Z about timer contact TR-la. Energization of the relay CR-Z causes the high heat breaker tap of the furnace to be energized through its normally open contact (not shown), the normally closed breaker contact (not shown) being opened to drop out the low heat breaker tap.

Coincident With completion of the high heat circuit A, the energization of control relay CR-l completes the solenoid circuit B through the normally open contact CR-lb of the relay as follows: Line 37, contact CR-lb, three minute timer contact TR1b (which closed three seconds before the other three minute contact TR-la), control relay contact CR-3b and line 38. The normally open contacts CR-3c and CR-Sd are closed, the former in part completing a lock-in solenoid energizing circuit and the latter in part completing the timed signaling circuit C through the warning horn 44 and light 45.

With the circuit in this condition, the one minute contacts TR-lc and TR1d of the main timer TR-l take over. Contact TR-lc, in closing, completes the circuit B through the solenoid 27 to energize the latter once each minute that the furnace is under high power. At the same time, with contact TR-ld closed, the horn 44 is sounded and the light 45 is illuminated once per minute; and these actions recur until the test rod 22 can again penetrate the more molten metal to open limit switch 34. In the resultant de-energization of breaker control relay CR2, as described above, the furnace is returned to low power. The cycle repeats when partial re-solidification of the metal bath prevents opening of the limit switch in the time required by relay TR-2.

The safety timer TR-3 is set for seven minutes and is energized each time the furnace goes into high heat power. After timing out, it opens its normally closed contact TR-Ea and closes its contact TR-3b. This Opens the circuit of breaker control relay CR-Z, returning the furnace to low power upon energization of the solenoid 42 of clutch 43. The selector switch 40 is then operated manually by turning it from on to off, then back to on, thus resetting the controls. At the time of timing out the horn 44 and signal light 45 are energized continuously through contact TR-3b, thus alarm-signaling a malfunction which should be corrected. It is seen that the timer TR-3 is a safety device which is energized only at times the furnace may remain for as long as seven minutes on high heat, after which the furnace is automatically switched to low heat by control relay CR-2.

The solidification control circuit 36 is very reliable. Built-in control and timing relays insure that the furnace is placed on high heat only when necessary, i.e., upon failure of the mechanism of FIGS. 1 and 2 to trip and open the limit switch 34 during the timed period of a sweep of feeler 22 in the molten bath. As long as the feeler can open switch 34 in the allotted time, the solenoid 27 will be periodically timed for repeated sweeps of feeler 22, but the breaker control relay will remain de-energized to keep the furnace on low heat. When the limit switch 34 remains closed, the system goes automatically into three minute timed phases at high heat, accompanied by one minute timed signals indicating the high heat phase and followed, if it persists too long, by a continuous alarm signal calling for attention to a possible malfunction.

The control circuit 36 can be built structurally into a very compact unit, and the mechanical components of FIGS. 1 and 2 are also very simple, compact and inexpensive of manufacture.

The drawings and the foregoing specification constitute a description of the improved solidification control device in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

1. A furnace melting control device to maintain the heating of a molten bath by a furnace within desired temperature limits in response to the varying fluidity of the bath as the result of temperature changes thereof, comprising a test member having means to mount the same in operative testing relation to said bath, said means including a fixed support adapted to be mounted in predetermined lateral relation to the bath, and an oscillatory arm pivotally mounted on said support to swing in a vertical plane, said test member being fixedly mounted on an end of said arm to be moved downwardly by the latter for a test sweep through said bath, which sweep is of varying time duration due to said varying fluidity of the bath, and means operating in response to variations in said time duration and operative to control the furnace and the resultant heating of the bath. I

2. The control device of claim 1, in which said test member is an elongated, downwardly bent one, the downwardly bent portion thereof being swept through the bath.

3. The control device of claim 1, in which said fixed support comprises a base, an upright fixed on and extending above said base and a horizontal part fixed to said upright and extending horizontally above said bath with said support so mounted relative to the bath, said oscillatoryarm being pivotally mounted on said horizontal part.

4. The control device of claim 2, in which said fixed support comprises a base, an upright fixed on and extending above said base and a horizontal part fixed to said upright and extending horizontally above said bath with said support so mounted relative to the bath, said oscillatory arm being pivotally mounted on said horizontal art. p 5. The control device of claim 4, and further comprising an electrical device carried by said base of said support to periodically actuate said arm for said downward sweep of said test member.

6. A furnace melting control device to maintain the heating of a molten bath by a furnace within desired temperature limits in response to the varying fluidity of the bath as the result of temperature changes thereof, comprising a test member having means to mount the samefor a test sweep through said bath, an electrical device to periodically actuate said test member for said sweep, which sweep is of varying time duration due to said varying fluidity of the bath, and means operating in response to variations in said time duration and operative to control the furnace and the resultant heating of the bath, said last named means including an electrical solidification control circuit variably operable in response to said duration of said sweep and adapted to be operatively connected to a furnace to regulate heating thereof.

7. The control device of claim 6, in which said control circuit includes a normally closed limit switch adapted to be opened by said test member in a predetermined time interval of said sweep.

8. The control device of claim 7, said control circuit further including timing and control relay means respectively determining said time interval and acting to energize said control circuit in the event said limit switch is not opened in said time interval, said circuit means being adapted to be operatively connected to the furnace to increase the heating thereof in said last named event.

9. A control circuit for a melting control device having a test member mounted for movement in a furnaceheated molten bath and variable in said movement in accordance with the heat of said bath, and an electric actuator having means to operatively connect the same to said test member to so move the latter, said control circuit acting to govern the heating of the bath by a furnace, said circuit comprising a limit switch adapted to be operated by said test member in the movement of the latter in said bath, a first control relay having means to electrically connect the same with said limit switch to be electrically energized when the latter is closed, said control relay being adapted to be operatively connected to the furnace to Vary the heating of said bath when said relay is closed, a first timing relay having a contact acting at least in part to complete a circuit connection between said switch and control relay when said timing relay is energized, a second control relay having contacts acting to complete said circuit connection when said second control relay is energized, and a second timing relay having a contact electrically connected to said second control relay to govern energization of the latter, said second timing relay being electrically connected to said limit switch for energization when the latter is closed, said second control and timing relays operating the contacts thereof to complete an energizing circuit through said first control relay when the limit switch is closed, thus to cause the furnace to vary the bath heat.

10. The control circuit of claim 9, in which said control circuit further comprises a lock-in relay electrically connected to said limit switch for energization when the latter is closed, said lock-in relay having contact means electrically connected to said switch and first control relay to furnish a holding circuit through the latter.

11. The control circuit of claim 9, in which said control circuit further comprises means providing a signaling circuit electrically energizable when said first control means is energizable, said signaling circuit comprising a signaling unit, said first timing relay having further 0 contact means electrically connected to said signaling unit to timedly energize the same when said first timing and control relays are energized.

12. The control circuit of claim 9, in which said control circuit further comprises means providing a signaling circuit electrically energizable when said first control means is energizable, said signaling circuit comprising a signaling unit, and a signal timing relay having contact means electrically connected to said signaling unit to energize the latter upon timing out of said signal relay.

13. The control circuit of claim 12, in which said first timing relay has further contact means electrically connected to said signaling unit to timedly energize the same when said first timing and control relays are energized.

14. The control circuit of claim 10, in which said control circuit further comprises means providing a signaling circuit electrically energizable when said first control means is energizable, said signaling circuit comprising a signaling unit, and a signal timing relay having contact means electrically connected to said signaling unit to energize the latter upon timing out of said signal relay, said first timing relay having further contact means electrically connected to said signaling unit to timedly energize the same when said first timing and control relays are energized.

15. The control circuit of claim 9, in which said first timing relay has a further contact acting at least in part to complete a circuit connection to said electric actuator when said timing relay is energized, and in which the operation of the contacts of said second control and timing relays acts both to cause the furnace to vary the bath heat and to cause the actuator to move the test member in the bath.

16. The control circuit of claim 15, and further comprising a lock-in relay electrically connected to said limit switch for energization when the latter is closed, said lock-in relay having contact means electrically connected to said switch and first control relay to furnish a holding circuit through the latter.

17. The control circuit of claim 15, and further comprising means providing a signaling circuit electrically energizable when said first control means is energizable, said signaling circuit comprising a signaling unit, said first time relay having further contact means electrically connected to said signaling unit to timedly energize the same when said first timing and control relays are energized.

18. The control circuit of claim 15, and further comprising means providing a signaling circuit electrically energizable when said first control means is energizable, said signaling circuit comprising a signaling unit, and a signal timing relay having contact means electrically connected to said signaling unit to energize the latter upon timing out of said signal relay.

19. The control circuit of claim 18, said first timing relay having further contact means electrically connected to said signaling uni-t to timedly energize the same when said first timing and control relays are energized.

20. The control circuit of claim 19, and further comprising a lock-in relay electrically connected to said limit switch for energization when the latter is closed, said lock-in relay having contact means electrically connected to said switch and first control relay to furnish a holding circuit through the latter.

21. A furnace melting control device for a furnace to maintain the heating of a molten furnace bath within desired temperature limits in response to the varying 4 9 10 member and operating in response to variations in said nected to the test member and responsive at its relay time duration to control the heat of the furnace and a means to said time duration variations. resultant maintenance of heating of the bath within said temperature 1 References Cited by the Examiner 22. The device of claim 21, in which said test member 5 U I STATES PATENTS is one having a linear sweep in said bath which represents 2 276 195 3/1942 Holmes. Sald test 2,421,819 6/1947 Vandenberg 62-139 23. The dev1ce of claim 21, 1n which said test member 2,717,496 9/1955 Andersson 62 138 is one having a linear sweep in said bath which represents 2 5 55 9 /1958 Baines 7 said test movement, said last named means including 10 electrical circuit and timing relay means operatively lcon- ALDEN D. STEWART, Primary Examiner. 

21. A FURNACE MELTING CONTROL DEVICE FOR A FURNACE TO MAINTAIN THE HEATING OF A MOLTEN FURNACE BATH WITHIN DESIRED TEMPERATURE LIMITS IN RESPONSE TO THE VARYING FLUIDITY OF THE BATH AS THE RESULT OF TEMPERATURE CHANGES THEREOF, COMPRISING A TEST MEMBER HAVING MEANS TO MOUNT THE SAME FOR A TEST MOVEMENT IN SAID BATH, SAID MOVEMENT BEING OF VARYING TIME DURATION DUE TO SAID VARYING FLUIDITY OF THE BATH, AND MEANS OPERATIVELY CONNECTED TO SAID TEST MEMBER AND OPERATING IN RESPONSE TO VARIATIONS IN SAID TIME DURATION TO CONTROL THE HEAT OF THE FURNACE AND A RESULTANT MAINTENANCE OF HEATING OF THE BATH WITHIN SAID TEMPERATURE LIMITS. 